Longitudinal study of cerebral blood flow regulation during exercise in pregnancy

Cerebrovascular adaptation to pregnancy is poorly understood. We sought to assess cerebrovascular regulation in response to visual stimulation, hypercapnia and exercise across the three trimesters of pregnancy. Using transcranial Doppler (TCD) ultrasound, middle and posterior cerebral artery mean blood velocities (MCAv(mean) and PCAv(mean)) were measured continuously at rest and in response to (1) visual stimulation to assess neurovascular coupling (NVC); (2) a modified Duffin hyperoxic CO2 rebreathe test, and (3) an incremental cycling exercise test to volitional fatigue in non-pregnant (n = 26; NP) and pregnant women (?rst trimester [n = 13; TM1], second trimester [n = 21; TM2], and third trimester [n = 20; TM3]) in total 47 women. At rest, MCAv(mean) and PETCO2 were lower in TM2 compared to NP. PCAv(mean) was lower in TM2 but not TM1 or TM3 compared to NP. Cerebrovascular reactivity in MCAv(mean) and PCAv(mean) during the hypercapnic rebreathing test was not different between pregnant and non-pregnant women. MCAv(mean) continued to increase over the second half of the exercise test in TM2 and TM3, while it decreased in NP due to differences in Delta PETCO2 between groups. Pregnant women experienced a delayed decrease in MCAv(mean) in response to maximal exercise compared to non-pregnant controls which was explained by CO2 reactivity and PETCO2 level.